A new mixed-valence lead(II) mangan­ese(II/III) phosphate(V): PbMn^II₂Mn^III(PO₄)₃

The title compound, lead trimanganese tris(orthophosphate), has been synthesized by hydro­thermal methods. In this structure, only two O atoms are in general positions and all others atoms are in the special positions of the Imma space group. Indeed, the atoms in the Wyckoff positions are namely: Pb1 and P1 on 4e (mm2); Mn1 on 4b (2/m); Mn2 and P2 on 8g (2); O1 on 8h (m); O2 on 8i (m). The crystal structure can be viewed as a three-dimensional network of corner- and edge-sharing PO₄ tetra­hedra and MnO₆ octa­hedra, building two types of chains running along the b axis. The first is an infinite linear chain, formed by alternating Mn^IIIO₆ octa­hedra and PO₄ tetra­hedra which share one vertex. The second chain is built up from two adjacent edge-sharing octa­hedra (Mn^II₂O₁₀ dimers) whose ends are linked to two PO₄ tetra­hedra by a common edge. These chains are linked together by common vertices of polyhedra in such a way as to form porous layers parallel to (001). These sheets are bonded by the first linear chains, leading to the appearance of two types of tunnels, one propagating along the a axis and the other along b. The Pb^II ions are located within the inter­sections of the tunnels with eight neighbouring O atoms in form of a trigonal prism that is capped by two O atoms on one side. The three-dimensional framework of this structure is compared with similar phosphates such as Ag₂Co₃(HPO₄)(PO₄)₂ and Ag₂Ni₃(HPO₄)(PO₄)₂.

SrMn^II₂Mn^III(PO₄)₃

The title compound, strontium trimanganese tris­(ortho­phosphate), was synthesized under hydro­thermal conditions. Its structure is isotypic to that of the lead analogue PbMn^II₂Mn^III(PO₄)₃. Two O atoms are in general positions, whereas all others atoms are in special positions. The Sr and one P atom exhibit mm2 symmetry, the Mn^II atom 2/m symmetry, the Mn^III atom and the other P atom .2. symmetry and two O atoms are located on mirror planes. The three-dimensional network of the crystal structure is made up of two types of chains running parallel to [010]. One chain is linear and is composed of alternating Mn^IIIO₆ octa­hedra and PO₄ tetra­hedra sharing vertices; the other chain has a zigzag arrangement and is built up from two edge-sharing Mn^IIO₆ octa­hedra connected to PO₄ tetra­hedra by edges and vertices. The two types of chains are linked through PO₄ tetra­hedra, leading to the formation of channels parallel to [100] and [010] in which the Sr^II ions are located. They are surrounded by eight O atoms in the form of a slightly distorted bicapped trigonal prism.

BaMn^II₂Mn^III(PO₄)₃

The title compound, barium trimanganese tris­(ortho­phosphate), was synthesized hydro­thermally. Its structure is isotypic with the lead and strontium analogues AMn^II₂Mn^III(PO₄)₃ (A = Pb, Sr). Except for two O atoms on general positions, all atoms are located on special positions. The Ba and one P atom exhibit mm2 symmetry, the Mn^II atom 2/m symmetry, the Mn^III atom and the other P atom .2. symmetry and two O atoms are located on mirror planes. The crystal structure contains two types of chains running parallel to [010]. One chain is linear and is composed of alternating Mn^IIIO₆ octa­hedra and PO₄ tetra­hedra sharing vertices; the other chain has a zigzag arrangement and is built up from two edge-sharing Mn^IIO₆ octa­hedra connected to PO₄ tetra­hedra by edges and vertices. The two types of chains are linked through PO₄ tetra­hedra into an open three-dimensional framework which contains channels parallel to [100] and [010] in which the Ba^II ions are located. The alkaline earth cation is surrounded by eight O atoms in the form of a slightly distorted bicapped trigonal prism.